Population and biodiversity insights
Homo sapiens became the first species to stop living inside local ecosystems. All other species, including our ancestral hominid ancestors, all pre-agricultural humans, and remnant hunter-gatherer societies still extant exist as semi-isolated populations playing specific roles (i.e., have “niches”) in local ecosystems. This is not so with post-agricultural revolution humans, who in effect have stepped outside local ecosystems. Indeed, to develop agriculture is essentially to declare war on ecosystems. -- Niles Eldredge
While the quote above remains valid, its emphasis on the transition to agriculture misses the potentially even larger issue of the shift from immediate-return to delayed-return subsistence. (See the "core ecological issues" page.)
It is critical we preserve biodiversity and protect the health of ecosystems. The web of life is Earth's life support system. Yet we are in the midst of the sixth mass extinction event in Earth's history. This one is human-caused. The following links should help in understanding these issues.
For resources to help you take action, see the "organizations and action" page.